Constructing a matrix based on different lists with Python

Question

I am going to make the following matrix:

 s= [[s11 s12 s13]
     [s21 s22 s23]
     [s31 s32 s33]]

where I can obtain each array of the matrix s by:

 sii = a(i)  ;  for s11, s22, and s33

 sij = a(i)**2 + 10    ;  for s12=s21, s23=s32, and s13=s31

here, ai is a list of data:

 a = [0.1, 0.25, 0.12]

So when I use the following:

import numpy as np 

s = np.ones([3,3])

def matrix(s):
a = [0.1, 0.25, 0.12]
s[np.diag_indices_from(s)] = ai
s[~np.eye(s.shape[0],dtype=bool)] = ai**2 + 10

It gives me an error. How can I solve this problem? Thanks.

utengr · Accepted Answer · 2017-10-28 15:38:47Z

1

Here is a hint for you on how to manipulate the diagonal and non-diagonal values.

import numpy as np

s = np.ones([3,3])

def matrix(s):
    a = [1,2,3]
    for i in range(len(a)):
        s[i,i] = a[i] #  sii = a(i) 
        rc = (i + 1) % len(a)
        val = a[i] ** 2 + 10 
        s[i, rc] = val # sij = a(i)**2 + 10 
        s[rc, i] = val # sij = a(i)**2 + 10 
    return s

print(matrix(s))

input:

[[ 1.  1.  1.]
 [ 1.  1.  1.]
 [ 1.  1.  1.]]

output:

[[  1.  11.   19.]
 [ 11.   2.  14.]
 [  19.  14.   3.]]

edited Oct 28, 2017 at 15:38

answered Oct 27, 2017 at 15:56

utengr

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14 Comments

Fara Over a year ago

Based on your answer, when I put ai = [0.1, 0.25, 0.12] instead of ai = 1, I don't get anything. Could you give me a hint how to input the list?

utengr Over a year ago

@Fara Can you please give an example of input and output matrices of how your output should look like? You can update your question with that.

utengr Over a year ago

@Fara do you want each element of the out matrix to be a Numpy array?

Fara Over a year ago

I am getting sii and sij (the arrays of the matrix s) as: sii= [0.1, 0.25, 0.12], which locate at the diagonal of matrix s, in total 3 of them, and sij = [0.5, 0.1, 0.2] that these locate at s21, s31, and s32. Here, s21=s12, s23=s32,.... Thanks for the help.

utengr Over a year ago

still not clear what you really want. Please update your question with a clear desired or expected output.

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